In a marine vessel, the energy to generate power to the propulsion unit or to other devices onboard is be stored into the marine vessel. In a seagoing vessel, fuel like oil is used as a source of energy and a diesel engine is used as a main engine. In a large marine vessel there may be several diesel engines that rotate generators or main propellers of the vessel. The fuel is delivered to the marine vessel in the harbors or during the voyage by fuel tankers. Other primary source of energy, like liquid natural gas has also been used.
The power production and propulsion system can be adjusted, controlled and monitored continuously to achieve the optimal efficiency. The power control is a part of the control system used to gain the result of the system. Likewise the propulsion system is controlled to produce power using the available electric and/or primary energy. In practice the sufficiency of the energy has not been as important as the efficiency of the devices and their control systems.
The power control of separate devices can allow for energy consumption efficiently and economically. This is valid for individual propulsion units, pumping devices, lighting and heating equipments. Further different kind primary energy sources can be used parallel and simultaneously. There may be different kind of fuels available and there may be several diesel engines that are driven parallel or sequentially depending on the power demand. All of these factors and the price of the fuel, the quality of the fuel and the availability of the fuel can affect overall energy efficiency of the marine vessel.
Published US patent application US2010/0023239 discloses a power demand management method, which determines the power demand on a power subsystem by optimizing a respective demand-dependent operating characteristic based on one or more operating conditions affecting the power subsystem.